Defects in heart formation during embryonic and fetal development likely contribute to miscarriages, which terminate up to 25% of all pregnancies, and Congential Heart Defects (CHDs), which are among the most common birth defects. Environmental factors may influence miscarriages and up to 80% of all CHDs, but little is known about how such chemicals affect formation of the heart during early embryonic differentiation. The goal of this SBIR project is to develop a Cardiopoiesis Assay (heart formation assay) to enable testing of compounds to determine if they influence the emergence of cardiac myocytes from multipotent mesodermal progenitors, a critical, early decision point, in heart formation. During the previous Phase I portion of the project, a version of the assay was developed using mouse embryonic stem cells, and this assay has proven useful in identifying chemicals, siRNAs, and miRs that modify cardiac differentiation. For Phase II, we propose to develop the assay using human induced pluripotent stem cells (hiPSCs), which will be derived from multiple donors to increase the genetic diversity represented by the assay. The Cardiopoiesis Assay will be useful in predicting whether chemical compounds affect heart formation in the human embryo, which is of critical importance to human health. The assay will be of interest to government agencies in the US (such as the Environmental Protection Agency) and worldwide, concerned with environmental toxicology.